There are numerous laboratory systems and medical, as well as pharmaceutical devices, in which it is important to determine the level in test tubes, titer plates and the like. Such a level determination is of importance particularly if it concerns the automation of measuring or test sequences.
A sample handler for liquids is known from the German utility model DE 29780368 U1. Metallic hollow needles are used in accordance with this utility model with one or two electrical conductors. The hollow needle is coated with an antiadhesive, electrically isolating layer inside and outside. The electrical conductors are designed in such a way that they have contact with the liquid only with a very small, non-isolated surface in order to be able to determine the immersing of the sample handler into the liquid.
A similarly constituted sample handler with level sensor is described in the German utility model DE 29609222 U1. This sample holder also comprises a hollow needle, which is coated with an antiadhesive, electrically isolating layer inside and outside. On this layer a conductive strip is applied.
The two sample handlers mentioned have the disadvantage that they do not allow for the making of a statement about the submergence of the sample handler in a liquid. The sample handlers permit recognition only of whether the sample handler has touched a liquid surface with its apex. In addition, the production is quite complex, since the isolating coating must be provided both on the inside and the outside of the hollow needle. Thus an application of the invention addressed by these two utility models on hollow needles with small inside diameter is particularly difficult.
Such a sample handler is thus not really suitable for the detection of the liquid level of small liquid quantities in small containers or buckets. Besides, no statement about the submergence of the sample handler can be made.
Another type of sample handler is described in the European patent application EP 670497 A1. This sample handler exhibits an inside and an exterior conductive tube, which are put into one another concentrically. The total structure is relatively complex and such sample handlers are probably expensive in the production.
In the European patent application EP 269837 A2 a sample handler is described, which comprises a non conductive tube on which two individual electrodes are fixed. This structure is also relatively complicated. In addition due to the complicated perimeter shape there is the danger of sample contamination, since drops can remain hanging on the sample handler and can thus be unintentionally transferred into another container.
Therefore it is an objective to provide an element for detecting a liquid level which is simple in the production and thin (in order to be able to work with this element even under restrained conditions, for example in arrays). In addition, an appropriate device is to be made available for the detection of a liquid level. Further, an exact statement about the submergence of the element is possible and the solution according to invention sample contamination.
These objectives are achieved according to invention by a rod-shaped element according to the claims, by a device with several rod-shaped elements according to the claims and by a device for determining a liquid level. Preferred embodiments are to be taken from the respective dependent claims.